1. Field of the Invention
This invention relates to packaging materials suitable for various photographic photosensitive materials, light-sensitive materials and electronic parts, particularly for relatively heavy materials among them, such as a roll film for movie.
2. Description of the Prior Art
As a packaging material for photographic photosensitive materials, it is necessary to have various properties including gas barrier, moistureproofness, antistatic property, rigidity, physical strength such as breaking strength, tear strength, impact puncture strength, Gelbo test strength and wear resistance, heat sealing properties such as heat seal strength, cut-seal ability, hot tack properties (hot-seal ability) and seal ability of contrasting materials, flatness, slipping character, low dusting characteristics, and the like. Generally, it is difficult to satisfy these properties by a single material. Therefore, the packaging material is usually composed of two or more layers. As the packaging material for rolls or sheets of photographic photosensitive materials, the inventor has already disclosed a packaging material of which physical strength is raised by combining two uniaxially stretched film layer (U.S. Pat. No. 4,331,725). Another packaging material suitable for heavy photosensitive materials is a triple layer laminated film composed of a foamed sheet and two uniaxially stretched thermoplastic resin films laminated on both sides thereof (U.S. Pat. No. 4,565,733). The thickness of the foamed sheet is 0.3 to 2 mm, and the expansion ratio is 5 to 50 times. Two uniaxially stretched films are bonded directly by heating or through an adhesive layer coated by hot melt coating so that respective molecular orientation axes cross with each other at an angle more than 30 degrees. The laminated film is compressed to 40 to 85% of the sum of respective layers. The triple layer laminated film is excellent in impact puncture strength and Gelbo test strength, and exhibits only a slight tendency to curl.
Since respective film layers are laminated by extrusion or using adhesive layer in the above packaging materials, they are curled and stiffened due to the lamination. Besides, when laminated films have a coextruded T die film or inflation film, a substantial amount of trimming loss occurs.